How to make a Particles Mountain
To make particles collide on the plane, add Collision Physics to it and set the stickiness to 1. Perhaps also add some friction.

The particles will now stop on the plane, but they won't pile to a mountain as you want. That is because particles don't collide with each other. See here for particle self collision.

Instead of particles, you may also try rigid body physics or water simulation (with enorm viscosity, don't know if that one will work though).